JP3958325B2 - Print medium coating liquid, ink jet ink, image forming method, set of print medium coating liquid and ink jet ink, and ink jet recording apparatus - Google Patents

Description

  The present invention relates to a printing medium coating liquid for applying a printing medium coating liquid to a part or the entire surface of a printing medium before or after an image is formed on at least a part of the printing medium by an inkjet recording method or the like. It is. The present invention also relates to an inkjet ink used in an inkjet recording method for recording an image by ejecting ink. The present invention also relates to an image forming method for forming an image using the printing medium coating liquid and the inkjet ink. Furthermore, the present invention relates to a set of the printing medium coating liquid and the inkjet ink. Furthermore, the present invention relates to an ink jet recording apparatus in which a set of the coating medium coating liquid and the ink jet ink is mounted.

  The ink jet recording method is a method for recording images, characters, and the like by ejecting micro droplets of ink and adhering them to a print medium (paper, etc.) according to various operating principles. It has features such as easy recording pattern flexibility, no need for development and fixing, and is rapidly spreading in various applications. However, when plain paper is used as a print medium, a curling phenomenon such as warping or curling may occur. This curling phenomenon is largely attributed to the application of moisture. That is, it has been found that the curling phenomenon occurs remarkably when the area to which moisture is applied is wide or when the applied amount is large.

  Several methods have been proposed in the past as methods for reducing and suppressing curling. For example, an ink-jet ink has been proposed that contains a solid substance that has four or more hydroxyl groups in the molecular structure and is soluble in water or an aqueous organic solvent (see, for example, Patent Document 1). Further, inks containing saccharides, sugar alcohols, and specific amide compounds as anti-curl agents have been proposed (see, for example, Patent Documents 2 to 5). An ink containing a combination of a specific polyhydric alcohol and glycerin has been proposed (see, for example, Patent Document 6). In addition, an ink containing a solvent, a polymer binder, a mordant, a water-soluble anti-curl compound, a water-soluble desizing compound, a light-resistant compound, an antifoaming agent, and the like has been proposed (see, for example, Patent Document 7).

As a means for forming an image using the ink jet recording method, a liquid (coating liquid) for improving the image is prepared separately from the normal ink jet ink as mentioned above, and the liquid is used as the ink. Various methods have been proposed for forming an image by adhering to a print medium prior to jetting the ink. For example, after applying a liquid composition containing polyvalent metal ions to a print medium in advance, printing an ink reactive with the liquid composition improves image characteristics such as image uniformity and image density. Has been proposed (for example, see Patent Documents 8 to 10).
JP-A-4-332775 JP-A-6-157955 JP-A-6-240189 JP-A-9-16539 JP 9-176538 A JP-A-10-130550 JP 2000-19826 A Japanese Patent Laid-Open No. 9-234944 Japanese Patent Laid-Open No. 11-115303 JP 2000-94825 A

  Curling can be suppressed to some extent by including a conventional curling-preventing compound in the ink. However, in recent years when high-speed printing and high image quality are required, there has been a demand for a coating liquid or ink that can more effectively reduce or suppress the curl phenomenon while improving ejection stability and reliability. In particular, in a system in which the print medium is applied to the entire surface of the print medium, and then the print medium is transported through the recording apparatus and then applied with ink, the ink is applied to the print medium coated with the print medium application liquid. In some cases, the print medium may curl during conveyance up to this time, leading to conveyance failure, and curling has been a major issue.

  Accordingly, it is an object of the present invention to provide a printing medium coating liquid that can reduce and suppress curling that occurs when a water-soluble component is applied to a printing medium.

  Another object of the present invention is to sufficiently suppress curling caused by leaving after printing on plain paper using ink-jet ink, and further, in a normal temperature and humidity environment, the printing start portion is disturbed at the start of printing. An object of the present invention is to provide an ink jet ink excellent in ejection stability in which no fading or the like occurs.

  Furthermore, another object of the present invention is to provide a coating liquid that achieves both the curl-suppressing effect when the printing medium coating liquid contains polyvalent metal ions and the storage stability as the printing medium coating liquid. is there.

  Furthermore, another object of the present invention is to suppress curling of a recorded matter obtained by a two-component system for forming an image using a printing medium coating liquid and an ink jet ink set.

The above object is achieved by the present invention described below. In other words, the print medium coating solution of the present invention contains a Mizu及beauty water-soluble organic compound, a coating solution for print medium used in inkjet printing medium, the water-soluble organic compound, multi having an amide bond Monohydric alcohol, polyethylene glycol having an average molecular weight of 200 to 300, polyethylene glycol having an average molecular weight of 1,000, N, N′-bis- (2-hydroxyethyl) -urea, bishydroxyethylsulfone, 1,2,6-hexanetriol , 1,5-pentanediol, 1,6-hexanediol, and a trimethylolpropane only water-soluble organic compound selected from the group, and the content of the water-soluble organic compound is a print medium coating solution It is characterized by being 15% by mass or more based on the total amount.

The ink jet ink of the present invention, a coloring material, an ink jet ink containing Mizu及beauty water-soluble organic compound, the water-soluble organic compound, a polyhydric alcohol having an amide bond, an average molecular weight of 200 to 300 Polyethylene glycol having an average molecular weight of 1,000, N, N′-bis- (2-hydroxyethyl) -urea, bishydroxyethylsulfone, 1,2,6-hexanetriol, 1,5-pentanediol, It is composed of only a water-soluble organic compound selected from the group consisting of 1,6-hexanediol and trimethylolpropane, and the content of the water-soluble organic compound is 15% by mass or more based on the total amount of the inkjet ink. It is characterized by that.

  The printing medium coating liquid of the present invention is a printing medium coating liquid used in combination with ink. In addition, the printing medium coating liquid and the inkjet ink of the present invention provide a step of applying an ink containing a coloring material in a dissolved or dispersed state to the printing medium, and a printing medium coating liquid is applied to the printing medium. It is the coating liquid for print media used for the image forming method which has a process, and the ink for inkjet.

  The image forming method of the present invention is an image forming method comprising a step of applying ink to a print medium, and a step of applying a print medium coating liquid to the print medium, wherein the ink is for ink jet as described above. It is an ink, and the printing medium coating liquid is the above-described printing medium coating liquid.

  Furthermore, as another embodiment of the present invention, a set of the printing medium coating liquid of the present invention and the inkjet ink of the present invention can be mentioned.

  Still another embodiment of the present invention is an ink jet recording apparatus using the printing medium coating liquid of the present invention and the ink jet ink of the present invention.

  In order to more effectively suppress curling after application of ink, it is preferable to contain polyvalent metal ions in the printing medium coating solution. Furthermore, it is more preferable that the inkjet ink and the printing medium coating liquid satisfy the following conditions.

(conditions)
The maximum absorption wavelength (color) in the visible region after mixing 50 g of the 800-fold diluted aqueous solution of the print medium and 0.3 g of the 5-fold diluted aqueous solution of the ink and filtering with a 0.2 μm filter after 15 minutes. When carbon black is used as the material, the absorbance at a wavelength of 550 nm) is (A), and the absorbance at the maximum absorption wavelength in the visible region of a mixed solution of 0.3 g of a 5-fold diluted aqueous solution of the inkjet ink and 50 g of pure water. When (B) is taken as (B), (A) and (B) satisfy the following relationship.
(A) / (B) <0.85
However, when polyvalent metal ions are contained in the printing medium coating solution, the printing medium coating solution changes due to storage, and a high optical density cannot be obtained, or the image quality obtained after the initial time and the lapse of time are different. May end up. For this reason, when polyvalent metal ions are contained in the printing medium coating solution, it is more preferable to contain a strong acid conjugate base and a weak acid conjugate base that provides a buffering action against changes in the hydrogen ion concentration.

  ADVANTAGE OF THE INVENTION According to this invention, the coating liquid for print media which can suppress generation | occurrence | production of curl by apply | coating to a print medium is obtained. In addition, regarding ink jet recording, curling can be sufficiently controlled, and in particular, printed matter on plain paper can be easily handled. In addition, an ink-jet ink can be obtained which can simultaneously achieve recording stability in the ink-jet recording method. Furthermore, even in a two-liquid system in which the print medium applied with the print medium coating liquid is transported through the recording apparatus and then applied with ink, the conveyance failure of the print medium applied with the print medium coating liquid is prevented. Furthermore, curling after ink application can be sufficiently suppressed. In addition, even when polyvalent metal ions are contained in the printing medium coating solution, a printing medium coating solution is provided that is excellent in storage stability of the printing medium coating solution and has no problem in liquid contact with equipment members. Is done. In other words, even when the printing medium coating solution is stored for a long period of time, it is possible to stably obtain a high-quality image with high color density and high color development without causing any back-through of the coloring material on the back side of the printing medium such as plain paper. It is done.

  Hereinafter, the present invention will be described in more detail with reference to preferred embodiments.

[Water-soluble organic compounds with water retention]
Since the curl after applying a liquid medium containing water to plain paper is considered to have some correlation with the evaporation of moisture applied to plain paper, the present inventors usually use ink for inkjet ink and coating liquid. The following detailed studies were conducted on the water retention of commonly used water-soluble organic compounds.

First, 20% by mass aqueous solutions of various water-soluble organic compounds were prepared, 10 g each was precisely weighed into a glass petri dish, and left in an environment at a temperature of 23 ° C. and a humidity of 45%. At the same time, pure water containing no water-soluble organic compound was also allowed to stand. As the water evaporates, the amount of solution in the petri dish decreases and the mass becomes constant over time. At the same time, the pure water-only petri dish that was allowed to stand at the same time has evaporated all the pure water. Therefore, the remaining water in the petri dish containing the water-soluble organic compound is retained by the water-soluble organic compound and the substance. The water retention capacity of each water-soluble organic compound in an environment of a temperature of 23 ° C. and a humidity of 45% was calculated by the following formula (1) .

さらに同一のシャーレを再度温度２３℃、湿度４５％の環境に移動させ、残存重量を測定し、水分保持力を同様に求めた。得られた結果を図７に示す。さらに両環境下での水分保持力の差を図８に示す。 Next, the petri dish is moved to an environment of temperature 30 ° C. and humidity 80%. Similarly, waiting for equilibrium to occur, the remaining weight under this environment is measured, and the moisture retention is expressed by the following equation (2) The water retention capacity of each water-soluble organic compound in an environment with a temperature of 30 ° C. and a humidity of 80% was determined.

Furthermore, the same petri dish was moved again to an environment of a temperature of 23 ° C. and a humidity of 45%, the remaining weight was measured, and the water retention capacity was similarly determined. The obtained results are shown in FIG. Further, FIG. 8 shows the difference in water retention between the two environments.

  The present inventors considered that there is some correlation between the difference in moisture retention force under the above-described environment and the occurrence of curling of plain paper. Then, when the aqueous solution containing the water-soluble organic compound examined above was applied to plain paper and the occurrence of curling was examined, the moisture retention in an environment of temperature 23 ° C. and humidity 45%, temperature 30 ° C., humidity 80 It has been found that water-soluble organic compounds having a difference in water retention in an environment of 36% or less significantly suppress curl. Therefore, an ink containing only a coloring material, an additive, and these water-soluble organic compounds was prepared, and the occurrence of curling was observed. As a result, it was confirmed that curling does not occur even after printing for several days at room temperature, leading to the present invention.

  Curl after printing on plain paper is because the moisture applied by the printing once enters between the hydrogen bonds between the fibers, and the tension applied at the beginning is loosened as the moisture moves due to evaporation, etc. It is thought that it occurs when only the printed part shrinks. It is assumed that water-soluble organic compounds whose moisture retention is difficult to change suppress the occurrence of curling because they are considered to hold a certain amount of moisture stably and therefore do not move as the moisture evaporates. To do.

  Further, as a result of further detailed investigation, a phenomenon was observed in which a water-soluble organic compound having a difference in water retention of 17.5% or more suppresses curling of printed matter for a longer period. It is speculated that water-soluble organic compounds with a difference in water retention of 17.5% or more have a weak hydrogen bonding force, so although they once enter the hydrogen bond between cellulose in paper, they migrate gradually and move. I think that.

  The water-soluble organic compound having water retention in the present invention is a water-soluble organic compound having a moisture retention of 5% or more in an environment of a temperature of 23 ° C. and a humidity of 45%, and further has a moisture retention of 6%. A water-soluble organic compound having a content of 23% or less is more preferable in terms of curling suppression effect.

According to the present invention, the water-soluble organic compound contained in the print medium coating solution has a water retention capacity in an environment at a temperature of 23 ° C. and a humidity of 45%, and a water retention in an environment of a temperature of 30 ° C. and a humidity of 80%. If the force difference is composed only of a water-soluble organic compound having a difference of 36% or less, the curl prevention effect of the present invention can be obtained. Specific examples of these water-soluble organic compounds include polyhydric alcohols having an amide bond, polyethylene glycol having an average molecular weight of 200 to 300; polyethylene glycol having an average molecular weight of 1000; N, N′-bis- (2-hydroxylethyl) -urea Bishydroxyethyl sulfone; 1,2,6-hexanetriol; 1,5-pentanediol ; 1,6-hexanediol; trimethylolpropane and the like. Among these, polyethylene glycol having an average molecular weight of 200, trimethylolpropane , and N, N′-bis- (2-hydroxylethyl) -urea are more preferable.

  The feature of the present invention is that the solvent or humectant constituting the coating medium coating liquid and the ink jet ink is composed only of the water-soluble organic compound having water retention as described above. The curling can be suppressed more efficiently than the ink. Furthermore, even when an image is formed as a set by combining the printing medium coating liquid and the ink, the use of the printing medium coating liquid of the present invention and further the ink jet ink makes it more efficient than the conventional ink set. It is possible to suppress curling.

[Coating liquid for print media]
The components, physical properties, the method of applying to the print medium, the amount of application, etc., which constitute the print medium coating solution according to the present invention will be described in detail.

(component)
The coating liquid for print media of the present invention has a water retention capacity of 36% or less, which is a difference between the moisture retention ability in an environment at a temperature of 23 ° C. and a humidity of 45% and the moisture retention ability in an environment of a temperature of 30 ° C. and a humidity of 80%. In addition to a certain water-soluble organic compound, an inorganic compound such as a polyvalent metal salt may be contained. By adding polyvalent metal ions to the printing medium coating liquid, the ink containing the coloring material dissolved or dispersed in the printing medium is applied, and then the printing medium coating liquid is brought into contact with the ink. By destabilizing the dissolved or dispersed state of the color material in the inside, it is possible to obtain good color material fixing properties, and it is possible to more effectively suppress curling of the recorded matter thus obtained. .

(Water-soluble organic compounds with water retention)
The water-soluble organic compound with water retention in the coating liquid for print media has a difference in water retention in an environment of temperature 23 ° C. and humidity 45% and moisture retention in an environment of temperature 30 ° C. and humidity 80%. The anti-curl effect of the present invention can be obtained if it comprises only 36% or less of a water-soluble organic compound. Specific examples of these water-soluble organic compounds include polyhydric alcohols having an amide bond ; polyethylene glycol having an average molecular weight of 200 to 300; polyethylene glycol having an average molecular weight of 1000; N, N′-bis- (2-hydroxylethyl) -urea Bishydroxyethyl sulfone; 1,2,6-hexanetriol; 1,5-pentanediol ; 1,6-hexanediol; trimethylolpropane and the like. Among these, polyethylene glycol having an average molecular weight of 200, trimethylolpropane , and N, N′-bis- (2-hydroxylethyl) -urea are more preferable.

  By containing a predetermined amount of the water-soluble organic compounds mentioned above, curling can be sufficiently suppressed. However, when means for applying the printing medium coating liquid of the present invention to a recording medium is used, means using an inkjet method or means for transferring using a plurality of rollers can be used to evaporate the printing medium coating liquid. Considering the accompanying adhesion between the inkjet head part or the rollers, it is preferable that at least one of the water-soluble organic compounds is liquid at room temperature (25 ° C.). Furthermore, a combination of trimethylolpropane having high water retention and a low molecular weight polyethylene glycol having a relatively low viscosity is more preferable.

(Polyvalent metal ions and their salts)
Specific examples of preferable polyvalent metal ions that can be used in the printing medium coating liquid according to the present invention include, for example, Ca ²⁺ , Cu ²⁺ , Ni ²⁺ , Mg ²⁺ , Zn ²⁺ , and Sr ^{2. Examples} include, but are not limited to, divalent metal ions such as ⁺ and Ba ²⁺ and trivalent metal ions such as Al ³⁺ , Fe ³⁺ , Cr ^3+, and Y ³⁺ . In order to contain these polyvalent metal ions in the coating liquid for a print medium, a polyvalent metal salt is used. The salt is a metal salt composed of the polyvalent metal ions as mentioned above and an anion that binds to these ions, but is required to be soluble in water. Preferable anions for forming the salt include conjugate bases of strong acids from the viewpoint of solubility. For example, NO ₃ ⁻ , SO ₄ ²⁻ , Cl ^{− which} are conjugate bases of nitric acid, sulfuric acid and hydrochloric acid which are strong acids are preferable. particularly NO ₃ ^- are preferable because of excellent solubility in water.

In addition, it was found that a strong acid salt containing a metal ion having a high ability to destabilize components in the ink tends to cause a decrease in pH. The present inventors used 4% by mass of a carbon black dispersion aqueous solution (dispersant: styrene-acrylic acid, acid value 200, mass% of dispersant / mass% of pigment = 0.2) for each polyvalent metal. When examined with ionic nitrates, Fe ³⁺ , Y ³⁺ , Al ³⁺ > Cu ²⁺ , Ca ²⁺ > Mg ²⁺ , Sr ²⁺ are highly destabilizing in order, and pH Decline was also likely to occur in this order. When using a salt composed of these polyvalent metal ions and a strong acid, the concentration of metal ions present in the coating medium coating solution is 0.2 mass% or more of Fe ³⁺ , Al ³⁺ and Y ³⁺ , In view of reactivity with ink, it is preferable to add 0.5% by mass or more of Ca ²⁺ and Cu ²⁺ and 1% by mass or more of Mg ²⁺ and Sr ²⁺ .

Also, in the salt with Mg ²⁺ and Sr ²⁺ having relatively low ability to destabilize the ink, an attempt is made to obtain the same ability as the Fe ³⁺ , Al ³⁺ and Y ³⁺ salt with higher ability. Then, it has been confirmed that the pH of the print medium coating solution tends to decrease with time.

In the present invention, the polyvalent metal ions include Ca ²⁺ , Mg ²⁺ , Sr ²⁺ , Al ^3+, and Y ³⁺ from the viewpoints of reactivity, colorability, and ease of handling. Particularly preferred is Ca ²⁺ .

  The content of polyvalent metal ions in the printing medium coating solution is preferably 0.01% or more and 10% by mass or less based on the total amount of the printing medium coating solution. More preferably, it is 1% by mass or more and 5% by mass or less, and in order to sufficiently exhibit the function of destabilizing the ink and to obtain a high level of image uniformity and optical density, it is 2 It is preferable to contain a polyvalent metal ion of not less than 4% by mass and not more than 4% by mass. It is also possible to include polyvalent metal ions exceeding 10% by mass in the printing medium coating solution. However, even if more than 10% by mass is added, there is a reason that a significant increase in the function of destabilizing the ink cannot be expected.

(Factors of changes due to storage)
However, when polyvalent metal ions are included in the print medium coating solution, the print medium coating solution changes due to storage, and a high optical density cannot be obtained, and the image quality obtained after the initial time and time are different. It turned out that there was a case. The cause of the above phenomenon is estimated as follows.

  For example, an acid group such as a carboxyl group reacts with a polyvalent metal ion generated by oxidation of an organic compound in a coating liquid for a print medium, and a counter ion (polyvalent metal anion) of the polyvalent metal ion and the acid group Protons generate acid to lower the pH of the print medium coating solution. If the pH fluctuates, the reactivity of the print medium coating solution changes, so the image quality obtained also changes. For example, if the reactivity of the printing medium coating liquid decreases, the color material penetrates into the print medium, so that a high optical density cannot be obtained, or the color material reaches the vicinity of the back side of the print medium. (So-called color material strike-through phenomenon).

  Therefore, the present inventors include both a strong acid conjugate base and a weak acid conjugate base that provides a buffering action against changes in the hydrogen ion concentration when polyvalent metal ions are contained in the coating medium coating solution. Therefore, the printing medium coating solution has a buffering action, and it is possible to minimize the above-described pH drop. In addition, since the metal ions derived from the buffer used to obtain a buffering action also contribute to the destabilization of the coloring material, a high optical density that cannot be obtained simply by using polyvalent metal ions is obtained. It is obtained. The pH in the present invention is a value measured at 25 ° C. by a conventional method.

(Conjugate base of weak acid)
In the present invention, “buffering action against change in hydrogen ion concentration” refers to hydrogen before and after the addition of nitric acid aqueous solution when adding 0.1 ml of 0.1 N nitric acid aqueous solution to 50 ml of the coating medium coating solution. The change in ion concentration is 1 × 10 ⁻⁴ or less (hereinafter referred to as “buffering action”). The change in hydrogen ion concentration can be calculated from the change in pH. The change in hydrogen ion concentration when the initial pH is a and the pH after addition of the aqueous nitric acid solution is b can be calculated from the following equation (hereinafter referred to as “change in hydrogen ion concentration”).
Change in hydrogen ion concentration (mol / L) = (10 ^−b ) − (10 ^−a )
In the present invention, in order to obtain a buffering effect, a conjugate base of a weak acid is included in the coating liquid for print media. Specific examples of the weak acid conjugate base include acetate ion, phosphate ion, carbonate ion, and phthalate ion. It is also possible to add a weak acid salt instead of adding a weak acid conjugate base. Specific examples of weak acid salts include acetates such as sodium acetate, potassium acetate and lithium acetate, hydrogen phosphates and bicarbonates, or hydrogen of polyvalent carboxylic acids such as sodium hydrogen phthalate and potassium hydrogen phthalate. A salt can be used. Furthermore, specific examples of the polyvalent carboxylic acid include malonic acid, maleic acid, succinic acid, fumaric acid, itaconic acid, phthalic acid, isophthalic acid, terephthalic acid, adipic acid, sebacic acid, dimer acid, Examples include pyromellitic acid and trimellitic acid.

(Physical properties)
The physical properties and coating conditions of the printing medium coating liquid are not particularly defined. However, polyvalent metal ions are included in the print medium coating liquid, and the print medium coating liquid is brought into contact with ink to destabilize the dissolved or dispersed state of the color material in the ink. When used as the printing medium coating liquid for a liquid system, it is preferable to define the physical properties of the printing medium coating liquid as follows in order to further suppress curling of the recorded matter to be obtained.

  The inventors of the present invention have disclosed a coating medium coating solution in which a color material is dissolved or dispersed in a print medium, and the dissolved or dispersed state of the color material in the ink by contacting the ink. As a result of investigation as a coating liquid for a print medium for a two-liquid system using in combination with a liquid composition containing a polyvalent metal ion to be destabilized, the degree of curling of the recorded matter obtained by the two-liquid system is It was found that the more color material aggregates in the medium are present in the surface layer, the more they are relaxed.

  The condition for allowing the aggregates to exist at a location where the agglomerates have penetrated slightly in the depth direction from the surface layer portion of the print medium includes controlling the reactivity of the print medium coating liquid and the ink. Furthermore, it is important that a sufficient amount of polyvalent metal ions for aggregating the coloring material is present within approximately 30 μm from the surface of the print medium. In order for a large amount of polyvalent metal ions contained in the print medium coating solution to be present within approximately 30 μm from the surface layer surface of the print medium, the amount of polyvalent metal ions contained in the print medium coating solution is Of course, it is considered that the penetrability of the printing medium coating liquid into the printing medium and the coating amount are greatly involved.

  The print medium coating liquid contacts the print medium and simultaneously penetrates along the fibers of the print medium under the influence of a solvent or a surfactant. Furthermore, it is presumed that the liquid that has permeated begins to evaporate simultaneously with this permeation, and a part of the polyvalent metal that has lost its dissolving power begins to precipitate. That is, by increasing the reactivity of the printing medium coating liquid with a small coating amount, penetration and evaporation of the liquid into the printing medium is promoted. As a result, it becomes possible to leave many multivalent metal ions at locations where they have penetrated slightly in the depth direction from the surface layer portion of the print medium.

From the above, in order to ensure more effective permeability of the coating liquid for printing media of the present invention containing polyvalent metal ions into plain paper, the Ka value obtained by the Bristow method is 1.3 mL · m ⁻² · msec ^−1/2 or more, coating amount is preferably 0.5 g / m ² or more and 5 g / m ² or less, more preferably Ka value is 3.0 mL · m ⁻² · msec ^−1/2 or more The conclusion was that the coating amount was 2.0 g / m ² or more and 3.0 g / m ² or less.

  Further, the pH of the printing medium coating solution is preferably 2 or more. If the pH is less than 2, the components in the printing medium coating solution may erode the surface of the member such as a tank or roller, and the components of the member may elute into the printing medium coating solution, which may adversely affect the image. Therefore, it is not preferable. It is preferable to maintain the pH of the printing medium coating solution in the range of 2 to 7, more preferably 3 to 6. Within this range, polyvalent metal ions can be more stably present in the printing medium coating solution, so that the reactivity of the printing medium coating solution can be sufficiently secured and sufficient buffering action can be obtained. Therefore, the long-term storage stability of the coating medium coating solution can be maintained.

  Furthermore, when the pH of the printing medium coating liquid is lower than the pH of the ink, the reaction between the ink and the printing medium coating liquid is more likely to occur more effectively, such as solid uniformity of the printed matter and strikethrough. From the viewpoint of

(Application method and application amount to print media)
Next, a method for applying the print medium coating liquid of the present invention to the print medium will be described in detail. Examples of the method for applying the printing medium coating liquid of the present invention to a printing medium include a coating method using a roller coating method, a bar coating method, a spray coating method, and the like. In addition, an ink-jet recording method is used in the same manner as ink, and an image forming area to which ink adheres and a coating method for selectively adhering a print medium coating liquid only in the vicinity of the image forming area are also possible.

  As a result of studying several methods for applying the above-mentioned printing medium coating liquid to a printing medium, the present inventors have made a two-liquid system in which a printing medium coating liquid contains a reactive agent such as a polyvalent metal ion. Especially when used as a coating liquid for printing media, the distribution state of polyvalent metal ions, which are reactive components in the vicinity of the surface area of the printing medium, becomes even more uniform than other means even with a small amount of application, and unevenness is observed after ink application. It came to the view that the roller coating method, which makes it possible to obtain excellent images without any problems, is the best.

  However, when a conventional coating liquid is applied to a print medium by a roller coating method, the liquid is applied to a wide range of the print medium, which easily causes a curl phenomenon. Further, in the case of a two-liquid system in which the print medium is transported in the recording apparatus after the conventional coating liquid is applied to the entire surface of the print medium and then ink is applied, the print medium is clogged in the middle of being transported in the recording apparatus. There was a phenomenon that would occur.

  Accordingly, the present inventors aimed to sufficiently suppress the curl phenomenon even with a small amount of coating medium coating solution applied, and as a result of further investigation, as a configuration of the printing medium coating solution of the present invention, water and The difference between the water retention capacity in an environment at a temperature of 23 ° C. and a humidity of 45% and the water retention capacity in an environment of a temperature of 30 ° C. and a humidity of 80% is 36% or less, and the content of the water-soluble organic compound Has reached a conclusion that it is preferably 15% by mass or more based on the total amount of the coating medium coating solution.

Even when the amount of the water-soluble organic compound is 15% by mass or less based on the total amount of the coating medium coating solution, curling can be suppressed to some extent when the amount applied to the printing medium is extremely large. However, when used as a print medium coating liquid for applying to a print medium before applying ink or after applying ink, considering the fixability of the printed portion after applying ink, the application amount is small. There is a need to do. Thus, in order to obtain a sufficient curling suppression effect even when the amount applied to the print medium is small, specifically, even when the amount is 3.0 g / m ² or less, the content of the water-soluble organic compound is It is necessary to be 15% by mass or more with respect to the total amount of the coating liquid for the print medium.

  Furthermore, it has also been found that the curl suppression effect is more efficiently exhibited by setting the water content to 77% by mass or less with respect to the total amount of the coating medium coating solution.

(Other ingredients)
The components used in the printing medium coating solution are surfactants in order to obtain a printing medium coating solution having desired physical properties as components other than water and polyvalent metal ions, water and water-retaining water-soluble compounds. An agent, an antifoaming agent, a preservative, an antifungal agent, and the like can be appropriately added within the range where the effects of adding these can be obtained and the object effects of the present invention are not impaired.

[Inkjet ink]
The components constituting the ink jet ink according to the present invention will be described in detail.

(component)
In addition to the water-soluble organic compound having water retention property, the ink of the present invention includes a surface active material for forming a coating material for a print medium having a color material, water, and, if necessary, desired physical properties. Consists of agents, antifoaming agents, antiseptics, antifungal agents, and the like The coloring material should be selected from water-soluble dyes, water-dispersible pigments (microencapsulated pigments, and further colored resins are also included in the scope of this specification) and combinations of two or more thereof. Can do. The amount of these color materials is not particularly limited, but is 0.1% by mass or more and 10% by mass or less in the ink. It is preferable to set the content to 1% by mass or more and 20% by mass or less in order to optimize various properties such as viscosity. Hereinafter, these color materials will be described in detail.

(Water-soluble organic compounds with water retention)
In order to suppress curling more effectively than the conventional ink-jet ink, the ink-jet ink of the present invention has a water retention capacity in an environment of a temperature of 23 ° C. and a humidity of 45%, and an environment of a temperature of 30 ° C. and a humidity of 80%. The water-soluble organic compound has a difference in water retention of 36% or less. In particular, when the water-soluble organic compound is contained in the ink, in order to satisfy many other performances as an ink-jet ink, a polyvalent having an amide bond having a molecular weight Mw in the range of 100 ≦ Mw ≦ 1000. Alcohol, polyethylene glycol having an average molecular weight of 200 to 300, polyethylene glycol having an average molecular weight of 1000, N, N′-bis- (2-hydroxylethyl) -urea, bishydroxyethylsulfone, 1,2,6-hexanetriol, 1, 5-pentanediol, 1,6-hexanediol, trimethylolpropane and the like are preferable. Among these, N, N′-bis- (2-hydroxylethyl) -urea is particularly preferable.

In addition, the molecular weight of the water-soluble organic compound having a molecular weight distribution such as the polyhydric alcohol and polyethylene glycol having the amide bond was an average molecular weight determined by any of the following.
(1) According to JIS handbook chemical analysis K0118 and K0123, mass spectrometry, gas chromatography mass spectrometry (GC-MS) method, and liquid chromatography mass spectrometry (LC-MS method) were performed to measure the molecular weight.
(2) For polyethylene glycol having a molecular weight distribution, the average molecular weight was determined from the size exclusion chromatography method (GPC method) in accordance with JIS Handbook Chemical Analysis K0124, and was used as the molecular weight.
(3) The molecular structure was determined and the molecular weight was determined.

  These water-soluble compounds can be used alone or in combination of two or more. In the present invention, in order to select and use a water-soluble organic compound having water retention in order to suppress curling, urea, glycerin, etc., which are usually used for imparting the ink with suitability as an inkjet ink The organic solvent is not used. Therefore, when the ink-jet ink according to the present invention is used in an ink-jet recording apparatus, it is preferable that the ink-jet ink has a configuration capable of suppressing ejection stability, nozzle clogging, and the like.

  Further investigation on this point revealed that among water-soluble compounds having a moisture retention of 36% or less, a polyhydric alcohol having an amide bond having a molecular weight Mw in the range of 100 ≦ Mw ≦ 1000, N, N Even at least one of '-bis- (2-hydroxylethyl) -urea and bishydroxyethyl sulfone is used, and preferably two or more types, more preferably three or more types are used together, so that even a high-speed inkjet head with small droplets The result was that it was fully usable. Among polyhydric alcohols having an amide bond with a molecular weight Mw in the range of 100 ≦ Mw ≦ 1000, one of two or three types to be combined may be N, N′-bis (2-hydroxylethyl) -urea. Most preferred. The reason for this is that N, N′-bis (2-hydroxylethyl) -urea has the ability to prevent association from a structure similar to urea. It is thought to make it easier to draw out performance such as prevention of clogging and dye solubility.

(Coloring material)
Examples of the color material used in the ink of the present invention include pigments such as carbon black and organic pigments. The pigments can be used alone or in combination of two or more. As the form of the pigment, a pigment dispersed with a dispersant, a self-dispersing pigment, colored fine particles / microcapsules, and the like can be used. These will be described in detail below.

Carbon black Specific examples of carbon black are carbon black pigments such as furnace black, lamp black, acetylene black, and channel black. For example, Raven 7000, Rayvan 5750, Rayvan 5250, Rayvan 5000, Rayvan 3500, Rayvan 2000 , Ray Van 1500, Ray Van 1250, Ray Van 1200, Ray Van 1190 ULTRA-II, Ray Van 1170, Ray Van 1255 (manufactured by Columbia), Black Pearls L, Legal 400R, Legal 330R, Legal 660R, Moguul ) L, Monarch 700, Monak 800, Monak 880, Monak 900, Mon 1000, Monak 1100, Monak 1300, Monak 1400, Valcan XC-72R (manufactured by Cabot), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Printex 140V, Special Black 6, Special Black 5, Special Black 4A , Special Black 4 (Degussa) 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. 2300, MCF-88, MA600, MA7, MA8, MA100 (manufactured by Mitsubishi Chemical Corporation) and the like can be used. Of course, it is not limited to these, and conventionally known carbon black can be used. Further, magnetic fine particles such as magnetite and ferrite, titanium black and the like may be used as the black pigment.

Organic pigments Specific examples of organic pigments include insoluble azo pigments such as toluidine red, toluidine maroon, Hansa yellow, benzidine yellow, pyrazolone red, soluble azo pigments such as lithol red, heliobordeaux, pigment scarlet, and permanent red 2B, alizarin, Derivatives from vat dyes such as indanthrone and thioindigo maroon, phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green, quinacridone pigments such as quinacridone red and quinacridone magenta, perylene pigments such as perylene red and perylene scarlet, isoindo Isoindolinone pigments such as linone yellow and isoindolinone orange, imidazolones such as benzimidazolone yellow, benzimidazolone orange and benzimidazolone red Pigments, pyranthrone pigments such as pyranthrone red, pyranthrone orange, thioindigo pigments, condensed azo pigments, thioindigo pigments, flavanthrone yellows, acylamide yellows, quinophthalone yellows, nickel azo yellows, copper azomethine yellows, perinones Other pigments such as orange, anthrone orange, dianthraquinonyl red, and dioxazine violet can be exemplified.

Moreover, the following can be illustrated when an organic pigment is shown by a color index (CI) number. Of course, conventionally known organic pigments can be used in addition to the above.
C. I. Pigment Yellow: 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 109, 110, 117, 120, 125, 128, 137, 138, 147, 148, 151, 153, 154, 166 168
C. I. Pigment Orange: 16, 36, 43, 51, 55, 59, 61
C. I. Pigment Red: 9, 48, 49, 52, 53, 57, 97, 122, 123, 149, 168, 175, 176, 177, 180, 192, 215, 216, 217, 220, 223, 224, 226, 227 228, 238, 240
C. I. Pigment Violet: 19, 23, 29, 30, 37, 40, 50
C. I. Pigment Blue: 15, 15: 1, 15: 3, 15: 4, 15: 6, 22, 60, 64
C. I. Pigment Green: 7, 36
C. I. Pigment Brown: 23, 25, 26
-Dispersant When using the above-described carbon black or organic pigment, it is preferable to use a dispersant in combination. As the dispersant, a dispersant that can stably disperse the above pigment in an aqueous medium by the action of an anionic group is suitably used. Specific examples of the dispersant include, for example, a styrene-acrylic acid copolymer, a styrene-acrylic acid-alkyl acrylate copolymer, a styrene-maleic acid copolymer, and a styrene-maleic acid-alkyl acrylate copolymer. Styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic acid alkyl ester copolymer, styrene-maleic acid half ester copolymer, vinyl naphthalene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer, A styrene-maleic anhydride-maleic acid half ester copolymer or a salt thereof is included. These dispersants preferably have a weight average molecular weight in the range of 1,000 to 30,000, particularly preferably in the range of 3,000 to 15,000.

Self-dispersing pigment As a coloring material, a pigment that can be dispersed in an aqueous medium without a dispersant by bonding an ionic group (anionic group) to the pigment surface, a so-called self-dispersing pigment can also be used. Examples of such pigments include self-dispersing carbon black. Examples of the self-dispersing carbon black include an anionic carbon black in which an anionic group is bonded to the surface of the carbon black.

Anionic carbon black Anionic carbon black has at least one anionic group selected from, for example, —COOM, —SO ₃ M, —PO ₃ HM, and —PO ₃ M ₂ bonded to the surface of carbon black. Things. In the above formula, M represents a hydrogen atom, an alkali metal, ammonium or organic ammonium. Among these, carbon black in which —COOM or —SO ₃ M is bonded to the carbon black surface and charged anionically has good dispersibility in the ink and can be particularly preferably used in the present invention.

  By the way, among those represented as “M” in the hydrophilic group, specific examples of the alkali metal include, for example, Li, Na, K, Rb and Cs, and specific examples of the organic ammonium include, for example, Examples include methylammonium, dimethylammonium, trimethylammonium, ethylammonium, diethylammonium, triethylammonium, methanolammonium, dimethanolammonium, and trimethanolammonium.

  The ink of the present invention containing self-dispersing carbon black in which M is ammonium or organic ammonium can further improve the water resistance of a recorded image, and can be particularly preferably used in this respect. This is considered to be due to the effect of ammonium being decomposed and ammonia being evaporated when the ink is applied onto the print medium. Here, the self-dispersing carbon black in which M is ammonium is, for example, a method of substituting self-dispersing carbon black in which M is an alkali metal with ammonium using an ion exchange method, or adding an acid to form H-type. And a method of adding M to ammonium by adding ammonium hydroxide.

  Examples of the method for producing anionic carbon black include a method in which carbon black is oxidized with sodium hypochlorite. By this method, a —COONa group can be chemically bonded to the surface of carbon black.

By the way, various hydrophilic groups as described above may be directly bonded to the surface of carbon black. Alternatively, another atomic group may be interposed between the carbon black surface and the hydrophilic group, and the hydrophilic group may be indirectly bonded to the carbon black surface. Specific examples of the other atomic groups include a linear or branched alkylene group having 1 to 12 carbon atoms, a substituted or unsubstituted phenylene group, and a substituted or unsubstituted naphthylene group. Here, examples of the substituent of the phenylene group and the naphthylene group include a linear or branched alkyl group having 1 to 6 carbon atoms. Also, specific examples of the combination of another atomic group and the hydrophilic group is, for _{example, -C 2 H 4 COOM, -Ph} -SO 3 M, -Ph-COOM , etc. (where, Ph represents a phenylene group) include It is done.

  By the way, in the present invention, two or more kinds of self-dispersing carbon blacks described above may be used as the ink coloring material appropriately selected. Further, the addition amount of the self-dispersing carbon black in the ink is preferably 0.1% by mass or more and 15% by mass or less, more preferably 1% by mass or more and 10% by mass or less with respect to the total amount of the ink. By setting this range, the self-dispersing carbon black can maintain a sufficiently dispersed state in the ink. Further, for the purpose of adjusting the color tone of the ink, a dye may be added as a coloring material in addition to the self-dispersing carbon black.

Colored fine particles / microencapsulated pigments In addition to the above-mentioned color materials, pigments microencapsulated with polymers, etc., and colored fine particles in which the periphery of resin particles is coated with a color material can also be used. Originally, microcapsules have dispersibility in an aqueous medium, but in order to improve dispersion stability, a dispersant as described above may further coexist in the ink. Moreover, when using colored fine particles as a coloring material, it is preferable to use the anionic dispersant described above.

(Aqueous medium)
As the ink used in the two-component system, the inkjet ink of the present invention, that is, the coloring material, water, and the water retention capacity in the environment of temperature 23 ° C. and humidity 45% and in the environment of temperature 30 ° C. and humidity 80%. By using an inkjet ink containing a water-soluble organic compound having a water retention difference of 36% or less, curling of the recorded matter can be further suppressed.

  However, even when a conventional ink (an ink that does not contain the water-retaining water-soluble organic compound of the present invention or contains an organic solvent other than the water-retaining water-soluble organic compound) is used, If the coating liquid for printing media of the present invention is used, curling can be suppressed far more than at least the conventional two-liquid system. Therefore, the ink for ink-jet recording of the present invention is not necessarily essential as the ink used in the two-component system of the present invention.

  Examples of the aqueous medium used in the ink composition when an ink other than the present invention is used include water or a mixed solvent of water and a water-soluble organic solvent. As the water-soluble organic solvent, those having an ink drying preventing effect are particularly preferable. Specifically, alkyl alcohols having 1 to 4 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol; dimethylformamide, dimethylacetamide Amides such as acetone, ketones or ketoalcohols such as acetone and diacetone alcohol, ethers such as tetrahydrofuran and dioxane, polyalkylene glycols such as polyethylene glycol and polypropylene glycol, ethylene glycol, propylene glycol, butylene glycol and triethylene glycol , 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol and other carbon groups having 2 to 6 alkylene groups Alkylene glycols containing: lower alkyl ether acetates such as polyethylene glycol monomethyl ether acetate; glycerin; multivalents such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether Lower alkyl ethers of alcohols; polyhydric alcohols such as trimethylolpropane and trimethylolethane; N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like. The above water-soluble organic solvents can be used alone or as a mixture. The water is preferably deionized water (ion exchange water).

  The content of the water-soluble organic solvent contained in the ink composition other than the present invention is not particularly limited, but is preferably in the range of 3% by mass to 50% by mass with respect to the total mass of the ink composition. The water content is preferably in the range of 50% by mass to 95% by mass with respect to the total mass of the ink composition.

(Other ingredients)
Furthermore, in addition to the above components, a moisturizing agent may be added as necessary, and a surfactant, an antifoaming agent, an antiseptic, an antifungal agent, in order to obtain a coating liquid for print media having desired physical properties. Etc. may be added as long as the effects of adding these are obtained and the object effects of the present invention are not impaired.

[Set of print medium coating liquid and inkjet ink]
The inventors of the present invention have conducted further studies with the aim of further improving the curl of a recorded matter obtained by a two-component system for forming an image using a printing medium coating liquid and an inkjet ink. It was found that the ink-jet ink and the printing medium coating liquid applied to the ink can more effectively suppress curling of the recorded matter obtained by satisfying the following conditions.

(conditions)
Maximum absorption in the visible region after mixing 50 g of an 800-fold diluted aqueous solution of the print medium coating solution with 0.3 g of a 5-fold diluted aqueous solution of the ink for ink and filtering with a 0.2 μm filter after 15 minutes. Absorbance at wavelength (when using carbon black as a color material, wavelength 550 nm) (A), maximum absorption in the visible region of a mixture of 0.3 g of a 5-fold diluted aqueous ink solution and 50 g of pure water When the absorbance at the wavelength is (B), (A) and (B) satisfy the following relationship.
(A) / (B) <0.85
The present inventors presume the mechanism by which the recorded matter obtained using the printing medium coating liquid and the ink jet ink defined as described above can more effectively suppress curling as follows. The above relational expression defines the reaction force between the printing medium coating liquid and the ink jet ink. By defining the reactivity as described above, most of the aggregates generated by the contact between the polyvalent metal ions contained in the coating liquid for the print medium and the color material contained in the ink-jet ink are printed media. Since it exists in a surface layer part, it is estimated that the shrinkage | contraction of the cellulose which occurs after a water | moisture content is provided can be suppressed.

  The print medium coating liquid and inkjet ink used in the two-component system are most effective for curling suppression of the recorded matter obtained by using the print medium coating liquid and inkjet ink of the present invention in combination. is there. However, even when the conventional ink is used, curling can be suppressed more effectively than at least the conventional two-liquid system when used in combination with the printing medium coating liquid of the present invention.

[Inkjet recording apparatus]
Next, an example of a recording apparatus for forming an image using the printing medium coating liquid and / or the inkjet ink will be described.

  FIG. 1 is a partial sectional view showing an example of an ink jet recording apparatus. This image forming apparatus employs a serial type ink jet recording system, and includes a recording head 1, a paper feed tray 17 for feeding a print medium (hereinafter also referred to as recording paper) 19, and a print of the present invention. A paper feed cassette 16 integrally formed with means for applying a medium coating liquid, drive means for reciprocating a recording head in a direction perpendicular to the recording paper conveyance direction, and driving of these components And control means for controlling.

  The recording head 1 is mounted on the carriage 2 so that the surface on which the ink discharge ports are formed is oriented toward the platen 11. Although not shown, the recording head 1 includes the ink discharge port, a plurality of electrothermal transducers (for example, heating resistance elements) for heating the ink liquid, and a substrate that supports the electrothermal transducer. The recording head 1 has an ink cartridge mounted in the carriage on the top thereof.

  The carriage 2 carries the recording head 1 and can reciprocate along two guide shafts 9 extending in parallel along the width direction of the recording paper 19. The recording head 1 is driven in synchronism with the reciprocating movement of the carriage and ejects ink droplets onto the recording paper 19 to form an image. The paper feed cassette 16 can be detached from the image forming apparatus main body. The recording paper 19 is stacked and stored on a paper feed tray 17 in the paper feed cassette 16. At the time of paper feeding, the uppermost sheet is pressed against the paper feed roller 10 by a spring 18 that presses the paper feed tray 17 upward. The sheet feeding roller 10 is a roller having a substantially half moon shape in cross section, and is driven and rotated by a motor (not shown) to feed only the uppermost sheet (recording paper 19) by a separation claw (not shown).

  The separated and fed recording paper 19 is transported along the transport surface of the paper feed cassette 16 and the transport surface of the paper guide 27 by the large-diameter intermediate roller 12 and the small-diameter application roller 6 in pressure contact therewith. Is done. These transport surfaces are formed by curved surfaces that draw a concentric arc concentric with the intermediate roller 12. Therefore, the recording paper 19 reverses its transport direction by passing through these transport surfaces. That is, the surface on which the recording paper 19 is printed is directed downward until it is conveyed from the paper feed tray 17 and reaches the intermediate roller 12, but when facing the recording head 1, it is directed upward (recording). Turn to the head side. Therefore, the printing surface of the recording paper always faces the outside of the image forming apparatus.

  The printing medium coating liquid coating means is provided in the paper feed cassette 16 and is provided with a replenishment tank 22 for supplying the printing medium coating liquid 15 and a part of the peripheral surface immersed in the tank 22. An intermediate roller 12 that is rotatably supported, and an application roller 6 that is arranged so as to be parallel to the intermediate roller and that contacts the intermediate roller 12 and rotates in the same direction. The application roller 6 is arranged so that the intermediate roller 12 for conveying the recording paper 19 and the peripheral surface are in contact with and parallel to each other. Therefore, when the recording paper 19 is transported, the intermediate roller 12 and the application roller 6 rotate with the rotation of the intermediate roller 12. As a result, the printing medium coating solution 15 is supplied to the peripheral surface of the coating roller 6 by the supply roller 13, and is further uniformly applied to the printing surface of the recording paper 19 sandwiched between the coating roller 6 and the intermediate roller 12. The coating liquid is applied by the supply roller 6.

  In the ink jet recording apparatus, the float 14 is provided in the replenishing tank 22. The float 14 is a substance having a lighter specific gravity than the print medium coating liquid 15 and floats on the liquid surface of the print medium coating liquid, thereby containing a reactive component from the outside through a remaining amount display window 21 which is a transparent member. The remaining amount of the coating liquid can be visually confirmed.

  FIG. 2 is a front view of the remaining amount display portion. The remaining amount display portion is provided with a display indicating the level of the remaining amount along the longitudinal direction of the remaining amount display window 21. In the figure, the case where the level of the printing medium coating liquid or the float 14 reaches the position indicated as “Full” is full. On the other hand, when the level of the print medium coating liquid or the float 14 is present at the position where “Add” is displayed, it indicates that there is little remaining printing medium coating liquid. Accordingly, it can be seen at a glance that the print medium coating solution 15 should be replenished when the print medium coating solution 15 gradually decreases and the float 14 is lowered to the Add line.

  As shown in FIG. 3, the replenishment method of the coating liquid composition for the print medium is constituted by a rubber member having a cut at the tip of the injection device 23 in a state where the paper feed cassette 16 is pulled out from the image forming apparatus main body. A printing medium coating solution is injected into the replenishing tank 22 by being inserted into the inlet 20.

  In this way, the recording paper coated with the printing medium coating liquid is then transported to the recording unit by a predetermined amount by the main transport roller 7 and the pinch roller 8 in pressure contact therewith, and the recording head 1 supplies ink. Is granted. The recording sheet 19 fed and printed in the above configuration is discharged and conveyed by the discharge roller 3 and the spur 4 in pressure contact with the discharge roller 3 and stacked on the discharge tray 5.

  In addition, when applying the printing medium coating liquid with a roller or the like, the ink is effectively destabilized with a small application amount, especially when the viscosity of the printing medium coating liquid is higher than the viscosity of the ink. This is preferable because it can be recorded and has good fixability of recorded matter.

  FIG. 4 shows another example of the ink jet recording apparatus. In FIG. 4, reference numeral 61 denotes a blade as a wiping member, one end of which is held and fixed by a blade holding member, and forms a cantilever. The blade 61 is disposed at a position adjacent to the recording area by the recording head 65, and in this example, is held in a form protruding in the moving path of the recording head 65.

  Reference numeral 62 denotes a cap on the projection port surface of the recording head 65, which is disposed at a home position adjacent to the blade 61, moves in a direction perpendicular to the moving direction of the recording head 65, contacts the ink ejection port surface, and performs capping. The structure to perform is provided. Further, reference numeral 63 denotes an ink absorber provided adjacent to the blade 61 and, like the blade 61, is held in a form protruding in the moving path of the recording head 65. The blade 61, the cap 62, and the ink absorber 63 constitute an ejection recovery unit 64, and the blade 61 and the ink absorber 63 remove moisture, dust, and the like from the ejection port surface. Further, the ink of the recording head, and the ink at the position of the discharge port of the coating liquid for the print medium are sucked by a pump (not shown) through a cap, so that the original ink or ink of the recording head And a recovery system unit that restores the original ejection performance of the printing medium coating liquid.

  Reference numeral 65 denotes a recording head which has discharge energy generating means and performs recording by discharging ink onto a print medium facing the discharge port surface on which the discharge port is arranged. Reference numeral 66 denotes a movement of the recording head 65 by mounting the recording head 65. It is a carriage for performing. The carriage 66 is slidably engaged with the guide shaft 67, and a part of the carriage 66 is connected to a belt 69 (not shown) driven by a motor 68. As a result, the carriage 66 can move along the guide shaft 67, and the recording area and its adjacent area can be moved by the recording head 65. 51 is a paper feeding unit for inserting a print medium, and 52 is a paper feed roller driven by a motor (not shown).

  With these configurations, the print medium is fed to a position facing the 65 discharge port surface of the recording head, and is discharged to a paper discharge portion provided with a paper discharge roller 53 as recording progresses. In the above configuration, when the recording head 65 finishes recording and returns to the home position, the cap 62 of the ejection recovery unit 64 is retracted from the moving path of the recording head 65, but the blade 61 protrudes into the moving path. As a result, the ejection port of the recording head 65 is wiped. When the cap 62 is in contact with the ejection surface of the recording head 65 to perform capping, the cap 62 moves so as to protrude into the moving path of the recording head. When the recording head 65 moves from the home position to the recording start position, the cap 62 and the blade 61 are at the same position as that at the time of wiping described above. As a result, the ejection port surface of the recording head 65 is wiped even during this movement.

  The above-mentioned movement of the recording head to the home position is not only at the end of recording or at the time of ejection recovery, but also to the home position adjacent to the recording area at a predetermined interval while the recording head moves the recording area for recording. Then, the wiping is performed with this movement.

  FIG. 5 shows an example of a member that supplies a print medium coating liquid that does not contain ink or color material to the recording head, for example, a cartridge 45 that contains ink or print medium coating liquid supplied via a tube. FIG. Here, reference numeral 40 denotes an accommodating portion, for example, a bag, in which supply ink or print medium coating liquid is accommodated, and a rubber stopper 42 is provided at the tip thereof. By inserting a needle (not shown) into the stopper 42, the ink in the bag 40 or the coating liquid for the print medium can be supplied to the head. Reference numeral 44 denotes an absorber that receives the waste ink or the waste print medium coating liquid. The container 40 is preferably made of a polyolefin, particularly polyethylene, on the liquid contact surface with the ink or print medium coating liquid. For example, as shown in FIG. 6, such a cartridge is configured to be detachable from a recording head 901 that discharges ink or a printing medium coating liquid, and when the cartridge 45 is mounted on the recording head. Ink or print medium coating liquid is supplied to the recording head 901.

[Ink characteristics; inkjet discharge characteristics, permeability to print media]
The set of the printing medium coating liquid and the inkjet ink according to the present invention is particularly preferably used for inkjet recording. Inkjet recording methods include a recording method in which droplets are ejected by applying mechanical energy to ink, and a recording method in which droplets are ejected by bubbling ink by applying thermal energy to the ink. The ink-jet ink of the invention and the coating liquid for print media can also be used. In that case, it is preferable that the above-described printing medium coating liquid and ink having a configuration according to the present invention have characteristics that enable ejection from an inkjet head. From the viewpoint of dischargeability from an inkjet head, the characteristics of these liquids are, for example, a viscosity of 1 to 15 mPa · s, a surface tension of 25 mN / m (dyne / cm) or more, particularly a viscosity of 1 to 5 mPa. -It is preferable that s and surface tension shall be 25-50 mN / m (dyne / cm). Furthermore, since the printing medium coating liquid of the present invention needs to react only with specific ink on a printing medium such as paper, the printing medium coating liquid is present at a location other than the recording portion with the specific ink. It is preferable that the surface tension of the print medium coating liquid is larger than that of the ink to be destabilized by the print medium coating liquid within a range that can be ejected from the inkjet head so as not to bleed. .

  Hereinafter, although it demonstrates more concretely using an Example and a comparative example, this invention is not limited at all by the following Example, unless the summary is exceeded. In the following description, parts and% are based on mass unless otherwise specified.

[Evaluation of coating liquid for print media]
(Preparation of coating solution for print media)
Each component was mixed according to the following Table 1, dissolved sufficiently by stirring, and then filtered under pressure with a micro filter (manufactured by Fuji Film) having a pore size of 1 μm to prepare coating medium coating solutions 1-16. The unit is mass%.

(With or without buffer action)
The pH of the obtained coating liquids for print media 4, 6 to 10, 14, and 15 was measured. Further, the pH when 1.0 ml of 0.1N aqueous nitric acid solution was added to 50 ml of the printing medium coating solution was measured, and the amount of change in the hydrogen ion concentration was measured. The presence or absence of action was examined. The results are shown in Table 2 below.

(Evaluation of curl)
After applying the obtained printing medium coating solutions 1 to 16 to the printing medium with a coating roller, the curled state was observed by the evaluation method described below. The speed of the roller and the contact pressure of the roller with the print medium were adjusted so that the amount of the print medium coating solution applied to the print medium was 2.4 g / m ² . In addition, Canon PB paper was used as the print medium. The curl evaluation method is as follows.

  The printed matter was left at a temperature of 24 ° C. and a humidity of 50% immediately after printing (within 1 minute), 1 hour later, 1 day, 2 days, 3 days, and 7 days, and then the curl amount was measured over time. When the printed paper was curled in the concave direction, it was defined as + (plus curl), and when it was curled in the convex direction, it was defined as-(minus curl), and the distance from the leading edge of the curled paper to the ground contact surface of the paper was measured with a ruler. . The curl criteria are as follows. The evaluation results are shown in Table 3 below.

AA: Within ± 10 mm A: Greater than ± 10 mm and within ± 25 mm B: Greater than ± 25 mm and within ± 40 mm C: State where the leading edge of the paper is warped inward or curled up

[Evaluation of ink]
(Preparation of ink)
Ingredients were mixed according to the following Table 4 and dissolved by sufficiently stirring, and then pressure filtered through a membrane filter (manufactured by Fuji Film) having a pore size of 0.2 μm to prepare inks 1 to 10. The unit is mass%.

(Preparation of pigment ink)
Next, pigment dispersions 1 and 2 shown below were prepared. A pigment ink was prepared using the obtained pigment dispersions 1 and 2. In preparing the pigment ink, the respective components were mixed according to Table 5 below, sufficiently stirred, and then pressure filtered through a membrane filter (manufactured by Fuji Film) having a pore size of 0.3 μm to prepare inks 11 to 13.

・ Pigment dispersion 1
As a pigment, 10 parts of Monac 880 (manufactured by Cabot), anionic polymer P-1 (styrene / M230G (methoxypolyethylene glycol methacrylate: Shin-Nakamura Chemical Co., Ltd.)) / Acrylic acid copolymer (copolymerization ratio (mass ratio)) = 65 / 12/25), acid value 160, weight average molecular weight 8,000, solid content 10% aqueous solution (neutralizing agent: potassium hydroxide) 40 parts and pure water 50 parts are mixed, and batch type vertical sand mill ( Aimex) was charged, 250 parts of 0.3 mm diameter zirconia beads were charged, and dispersion treatment was performed for 10 hours while cooling with water. Further, this dispersion was centrifuged to remove coarse particles. As a final preparation, Pigment Dispersion 1 having a solid content of about 14.0% and a weight average particle size of 110 nm was obtained.

・ Pigment dispersion 2
10 parts of Monac 880 (manufactured by Cabot) as a pigment, anionic polymer P-2 (styrene / acrylic acid copolymer (copolymerization ratio (mass ratio) = 70/30), acid value 180, weight average molecular weight 10,000 , 40 parts of solid content aqueous solution, neutralizing agent: potassium hydroxide (40 parts) and pure water (50 parts) were mixed, charged into a batch type vertical sand mill (manufactured by IMEX), and filled with 150 parts of 0.3 mm diameter zirconia beads. Then, the dispersion treatment was performed for 10 hours while cooling with water. Further, this dispersion was centrifuged to remove coarse particles. As a final preparation, Pigment Dispersion 2 having a solid content of about 14% and a weight average particle size of 110 nm was obtained. An aqueous solution of anionic polymer P-3 (ethyl acrylate / acrylic acid copolymer (copolymerization ratio (mass ratio) = 87/13), acid value 100, weight average molecular weight 11,000, solid content 10%) in the dispersion. (Neutralizer: potassium hydroxide)) 30 parts were added to obtain pigment dispersion 2.

(Evaluation of curling and ejection stability)
The inks 1 to 13 were applied to a print medium using an inkjet recording apparatus having an on-demand type multi-recording head that ejects ink by applying thermal energy corresponding to a recording signal to the ink. The ink jet recording apparatus used has a recording density of 2.8 pL per dot, a recording density of 2400 × 1200 dpi, and the driving condition is a device with a driving frequency of 10 kHz, and A4 full solid (20 × 25 cm). A color image was formed. The print medium used for the evaluation is A4 size PPC paper (manufactured by Canon). Further, printing is performed by two-pass printing in which the printing area is scanned twice, and the amount of ink jet ink applied to the print medium is 12.5 g / m ² .

Curling evaluation method The ink curling evaluation method is the same as that when the coating medium coating solution 15 is used. The evaluation results are shown in Table 6 below.

・ Evaluation method of ejection stability (startup characteristics) In order to evaluate the ejection stability of ink, it was confirmed in a normal temperature and humidity environment that there was no disturbance or blurring of the print start area at the start of printing. The criteria for discharge stability (startup characteristics) are as follows. The evaluation results are shown in Table 6 below.

A: There is no blur B: The export part is slightly faded C: The export part is greatly faded

[Curl evaluation of recorded matter obtained by two-component system]
Next, after applying the printing medium coating liquid, the curl of the recorded matter obtained in the ink application system (two liquid system) was confirmed. Further, the print medium coating solution is stored for a long period of time, and the print medium coating solution before and after storage is used as the print medium coating solution for the system to form an image. It was confirmed.

(Preparation of recorded material in a two-component system)
The printing medium coating liquids 1 and 10 were applied to the printing medium by a roller coating method using the coating roller having the configuration shown in FIG. 1 as the printing medium coating liquid. The speed of the roller and the contact pressure of the roller with the print medium were adjusted so that the amount of the print medium coating solution applied to the print medium was 2.4 g / m ² . The print medium used was Canon PB paper (A4 size).

Ink 1, 3, 4 using an ink jet recording apparatus having an on-demand multi-recording head that ejects ink by applying thermal energy according to a recording signal to the ink immediately after applying the coating liquid for printing medium. 6-9, 11-13, and the following evaluation was performed. The ink jet recording apparatus used has a recording density of 2.8 pL per dot, a recording density of 2400 × 1200 dpi, and the driving condition is a device with a driving frequency of 10 kHz, and A4 full solid (20 × 25 cm). A color image was formed. The print medium used for the evaluation is A4 size PPC paper (manufactured by Canon). Further, the printing is performed by two-pass printing in which the printing area is scanned twice, and the adhesion area of the inkjet ink to the print medium is 12.5 g / m ² .

(Reactivity of ink and print medium coating solution)
Using the following print medium coating liquid and ink set, mixing was performed under the following conditions, absorbance was measured, and reactivity was evaluated. The results are shown in Table 7 below.

  The absorbance at 550 nm after mixing 50 g of an 800-fold diluted aqueous solution of a printing medium coating solution with 0.3 g of a 5-fold diluted aqueous solution of ink and filtering with a 0.2 μm filter after 15 minutes is (A), The absorbance at 550 nm of a mixed solution of 0.3 g of a 5-fold diluted aqueous solution of ink and 50 g of pure water was defined as (B), and the value of (A) / (B) as a reactivity index was obtained. The inks 1, 3, 4, and 6 containing no pigment as a coloring material in the ink were mixed with the print medium coating solution by the same method as described above, but the values (A) / (B) Was 1 and showed no reactivity at all.

(Evaluation of curl)
The curl evaluation method is the same as that when a printing medium coating solution is used. The evaluation results are shown in Table 8 below.

(Evaluation of image change by storage)
After applying the print medium coating liquids 4, 6 to 10, 14, and 15 to the print medium, the ink 11 is solidly printed with a width of 2 × 2 cm on the center of the print medium, and the color is printed from the back side of the print surface. The back of the material was visually observed to measure the print density on the front side of the print surface. In addition, using a printing medium coating solution that was hermetically stored in a 60 ° C. oven for one month, the back-through of the coloring material was observed and the density was measured in the same procedure.

The change in image quality before and after storage of the printing medium coating solution was evaluated according to the following criteria. The ink jet recording apparatus used had a recording density of 2.8 pL per dot, a recording density of 2400 × 1200 dpi, and a driving condition was a device with a driving frequency of 10 kHz. Further, the roller speed and the contact pressure of the roller to the printing medium coating liquid were adjusted so that the coating amount of the coating liquid for the printing medium was 2.4 g / m ² . The evaluation criteria for the evaluation image quality change are as follows. The evaluation results are shown in Table 9 below.

  A: Compared with the comparative example, there is almost no change in the degree of strikethrough and no change in density.

  B: Either the change in the degree of strikethrough or the change in density is equal to or higher than that in the comparative example.

  C: The degree of show-through and the change in density are equal to or higher than those in the comparative example.

  Furthermore, when the same evaluation as the evaluation of the image change by the above storage was performed using each reaction solution after being stored in a 60 ° C. oven for one month, Examples 25 to 27 were backed by reactivity before and after storage. Although there was no difference in the detachability, in Comparative Examples 10 and 11, the degree of show-through changed before and after storage.

It is a schematic sectional side view which shows an example of an inkjet recording device. FIG. 2 is a front sectional view of a liquid composition remaining amount display unit provided in the ink jet recording apparatus of FIG. 1. FIG. 2 is a schematic sectional side view showing a replenishment state of a liquid composition to the ink jet recording apparatus of FIG. 1. It is a schematic perspective view which shows an example of an inkjet recording device. It is a longitudinal cross-sectional view which shows an example of an ink cartridge. FIG. 2 is a schematic plan view showing a state where an ink cartridge is mounted on a recording head. It is a figure which shows the measurement result (difference by an environment) of the moisture retention of a water-soluble organic compound. It is a figure which shows the difference of the water | moisture-content retention of a water-soluble organic compound.

Explanation of symbols

1: Recording head 2: Carriage 3: Paper discharge roller 4: Spur 5: Paper discharge tray 6: Application roller 7: Main transport roller 8: Pinch roller 9: Guide shaft 10: Paper feed roller 11: Platen 12: Intermediate roller 13 : Supply roller 14: Float 15: Liquid composition 16: Paper feed cassette 17: Paper feed tray 18: Spring 19: Recording medium (recording paper)
20: injection port 21: remaining amount display window 22: replenishment tank 23: injection device 27: paper guide 40: bag 42: stopper 44: absorber 45: ink cartridge 51: paper feed unit 52: paper feed roller 53: paper discharge Roller 61: Blade 62: Cap 63: Ink absorber 64: Ejection recovery unit 65: Recording head 66: Carriage 67: Guide shaft 68: Motor 69: Belt 901: Recording head

Claims (15)

Containing Mizu及beauty water-soluble organic compound, a coating solution for print medium used in inkjet printing medium,
The water-soluble organic compound is a polyhydric alcohol having an amide bond, polyethylene glycol having an average molecular weight of 200 to 300, polyethylene glycol having an average molecular weight of 1,000, N, N′-bis- (2-hydroxyethyl) -urea, bis Composed of only a water-soluble organic compound selected from the group consisting of hydroxyethyl sulfone, 1,2,6-hexanetriol, 1,5-pentanediol, 1,6-hexanediol, and trimethylolpropane;
And the content of the said water-soluble organic compound is 15 mass% or more with respect to the coating-medium coating liquid whole quantity, The printing-medium coating liquid characterized by the above-mentioned.   Furthermore, the coating liquid for print media of Claim 1 containing a polyvalent metal ion.   Furthermore, the coating liquid for print media of Claim 1 or 2 containing the conjugate base of a strong acid and the conjugate base of a weak acid. Print media coating liquid according to any one of claims 1 to 3 in front Kisui soluble organic compound containing two or more. Print media coating liquid according to any one of claims 1 to 3 including pre Kisui soluble organic compound 3 or more. The print medium coating solution according to any one of claims 1 to 5 , wherein the water content is 77% by mass or less based on the total amount of the print medium coating solution. The ink print according to any one of claims 1 to 6 , wherein a method of applying the print medium coating liquid to an inkjet print medium is a roller coating method, a bar coating method, a spray coating method, or an inkjet recording method. Medium coating solution. Colorant, an ink jet ink containing Mizu及beauty water-soluble organic compound,
The water-soluble organic compound is a polyhydric alcohol having an amide bond, polyethylene glycol having an average molecular weight of 200 to 300, polyethylene glycol having an average molecular weight of 1,000, N, N′-bis- (2-hydroxyethyl) -urea, bis Composed of only a water-soluble organic compound selected from the group consisting of hydroxyethyl sulfone, 1,2,6-hexanetriol, 1,5-pentanediol, 1,6-hexanediol, and trimethylolpropane;
An ink-jet ink, wherein the content of the water-soluble organic compound is 15% by mass or more based on the total amount of the ink-jet ink. The inkjet ink according to claim 8, the front Kisui soluble organic compound containing two or more. The inkjet ink according to claim 8 before including Kisui soluble organic compound 3 or more. 11. An image forming method comprising a step of applying ink to a print medium and a step of applying a print medium coating liquid to the print medium, wherein the ink is for inkjet according to claim 8 . an ink, and an image forming method, wherein the printing medium coating liquid is a printed medium coating solution according to item 1 to any one of claims 1 to 7. A print medium comprising a set of a print medium coating liquid and an inkjet ink, wherein the print medium coating liquid is the print medium coating liquid according to any one of claims 1 to 7. Set with coating liquid and inkjet ink. A set of a printing medium coating liquid and an inkjet ink, wherein the inkjet ink is the inkjet ink according to any one of claims 8 to 10. And a set with inkjet ink. A set of a printing medium coating liquid and an inkjet ink, wherein the printing medium coating liquid is the printing medium coating liquid according to any one of claims 1 to 7 , wherein the inkjet ink is used. A set of a coating liquid for a print medium and an inkjet ink, which is the inkjet ink according to any one of claims 8 to 10 . An ink jet recording apparatus characterized by the inkjet ink is mounted according to any one of the print medium coating solution for the claims 8 to 10 according to any one of claims 1 to 7.

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